<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>id选择器</title>

    <style>
        body{
            /* 10px = 1em */
            font-size: 62.5%;
        }
        #d1{
            background-color: #999;
            height: 10em;
            width: 50%;
        }
        #d2{
            background-color: green;
            height: 12em;
            width: 65%;
        }
    </style>
</head>
<body>
    <div id="d1">div1</div>
    <div id="d2">div2</div>
</body>
</html>